1. Technical Field
The present invention relates to imaging of objects using x-ray backscattering techniques.
2. Description of Related Art
A large market exists for modification of structures and systems within military and commercial aircraft. The modification process involves reverse engineering of the aircraft to identify structures and systems that are to be modified. One challenge faced by modification engineers is uncertainty about the locations and configurations of structures and systems that are hidden from view. For example, flight-ready, fielded aircraft have many structures and systems that are obscured by exterior skins and interior furnishings and closure panels. Often, legacy data such as drawings, planning and tooling are insufficient to determine present configurations of structures and systems. Legacy data also does not typically include information about hidden foreign objects or debris.
Some conventional techniques for determining the locations and configurations of hidden aircraft structures and systems during modification procedures include digital photography, panoramic cameras, and line-of-sight reverse engineering. These methods have significant drawbacks, such as requiring partial disassembly of the subject aircraft in order to expose the hidden structures/systems. This process is labor intensive and therefore quite expensive. Furthermore, only after the disassembly has been completed can the process of planning the modifications begin. The need for disassembly thus lengthens the timeframe for aircraft modification, which in turn increases the cost of the process. Furthermore, conventional systems and methods lack verified definition data for each aircraft going through modifications.
One method for analyzing structures involves x-ray backscattering. Conventional x-ray backscatter systems comprise an x-ray tube that generates photons, and at least one solid-state detector or photo-multiplier tube. Photons emerge from the source in a collimated “flying spot” beam that scans vertically while the system is moved horizontally. Backscattered photons are collected in the detector(s) and used to generate two-dimensional and/or three-dimensional images of objects hidden behind coverings.
X-ray backscattering systems are currently used to scan trucks and railroad cars for contraband. For example, at a border crossing an x-ray backscatter image may help border officials to spot people or drugs hidden in secret compartments. The systems in use in such applications are mounted in large vans. The collimated beam scans vertically while the van drives alongside the truck or railcar. The detector(s) remain at a constant distance from the scanned object as the van drives.
The large size of these van-mounted systems makes them unsuitable for use in interior spaces, such as inside an aircraft (except, perhaps, inside large cargo aircraft having ramp doors). Furthermore, in order for an x-ray backscatter to produce a distortion-free image, the photon detector must be equidistant from all portions of the object being scanned. Thus, while van-mounted systems are well-adapted for producing images of trucks or railcars, which generally have vertical side walls, aircraft fuselages are generally cylindrical and have oval or elliptical cross-sections. As a collimated beam scans such a surface, some portions of the surface are located closer to the photon detector(s) than other portions. The variations in distance from the detector(s) produce distortions in the backscattered image. Such distortions present a minor inconvenience when searching for contraband, where the goal is merely to identify the presence of foreign objects to determine whether a closer investigation is warranted. In a reverse engineering application, however, distortions present a major problem. Before modification engineers can begin to develop a modification plan, they must have an image that meets a certain threshold in accurately identifying the locations, sizes and configurations of hidden structures and systems. Current systems do not meet this threshold.
Conventional x-ray backscatter systems are also not able to account for objects within an aircraft, such as galleys, cabinets and seats. Further, these systems do not have adequate scanning speed, robustness, ability to work in various orientations, scanning range, or field of view for aircraft reverse engineering applications. They are also not tailored to detect and accurately depict the materials present on aircraft.